This work will investigate the potential of a nanoporous silicon membrane (pnc-Si) to provide revolutionary filtration of macromolecules based on their size and charge. Because the novel membrane material is molecularly thin (15 nm), it is predicted to improve the efficiency of both diffusion and convective flow based separations. Because the material is made from silicon, manufacturing is scalable, readily integrated into microfluidic devices, and amenable to surface modifications could make membrane permeability controllable through an externally controlled voltage. The material may enable a host of small scale analytical, preparative and therapeutic devices. Aim 1: Quantitatively characterize the performance of pnc-Si membranes for diffusion- based separations we will quantify the function of pnc-Si membranes in diffusion-based separations. Using a membrane library with a range of porosities and pore sizes, we will determine: 1) rejection sizes of model species and protein mixtures; and 2) the mobility of small solutes, model particles, and proteins through pnc-Si membranes. Work will directly address the potential deleterious effects of protein adsorption by measuring small solute transport in the presence and absence of high protein concentrations. Membranes will be directly inspected for evidence of bio-fouling by transmission electron microscopy. If protein adsorption slows transport, membranes will be modified by grafting with short PEG molecules, and the modified membranes re-characterized. Aim 2: Quantitatively characterize pnc-Si membranes for charged-based separations Here we will characterize the ability of pnc-Si membranes to separate macromolecules based on charge. We will measure diffusive transport of charged dyes in solutions of different ionic strength. We will quantify results using as-prepared membranes and membranes that we modify to carry permanent negative or positive charge, Results will be interpreted in the context of Debye-Huckel theory. We will then examine the importance of membrane charge on protein transport by modulating solution pH around the isoelectric point of albumin. Finally, will coat pnc-Si membranes with noble metals with the goal of actively adjusting membrane permeability through external control over membrane charge. This project will characterize the ability of a new silicon-based, nanoporous membrane to selectively filter macromolecules based on size and charge. The molecularly thin nanomembranes have the potential to revolutionize filtration rates and are the first filter material that can be integrated into microfluid systems as modules. These abilities are expected to enable a host of new small scale clinical and diagnostic devices. [unreadable] [unreadable] [unreadable]